Articles having elevated temperature elasticity made from irradiated and crosslinked ethylene polymers and method for making the same

ABSTRACT

The present invention relates to elastic articles comprising a crosslinked or crosslinkable ethylene polymer and a method for making the same. In particular, the invention relates to a shaped article (e.g. film or fiber) characterized by improved elasticity at elevated temperatures and comprising a substantially cured, irradiated, or crosslinked (or curable, irradiated or crosslinkable) homogeneously branched ethylene polymer. The improved elastic article of the present invention is particularly suitable for use in applications where good elasticity must be maintained at elevated temperatures such as, for example, personal hygiene items and disposable infection-control garments at body temperatures of about 100° F. (38° C.).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.09/313,740, filed May 18, 1999 now U.S. Pat. No. 6,500,540; which claimspriority benefit of U.S. Provisional Application Serial No. 60/086,059,filed May 18, 1998, expired.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of provisional applicationNo. 60/086059, field May 18, 1998, the disclosure of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a crosslinked, heat resistant elasticarticle having elevated temperature elasticity comprising a cured,irradiated or crosslinked ethylene polymer and a method for making acrosslinked, heat resistant elastic article. In particular, theinvention relates to a shaped article (e.g. film or fiber) characterizedby heat resistance and improved elasticity at elevated temperatures andcomprising a substantially cured, irradiated, or crosslinkedhomogeneously branched ethylene polymer. The improved elastic article ofthe present invention is particularly suitable for use in applicationswhere good elasticity must be maintained at elevated temperatures suchas, for example, personal hygiene items and disposable infection-controlgarments at body temperatures of about 100° F. (38° C.).

BACKGROUND OF THE INVENTION

Materials with excellent stretchability and elasticity are needed tomanufacture a variety of disposal and durable articles such as, forexample, incontinence pads, disposable diapers, training pants, sportapparel and furniture upholstery. Stretchability and elasticity areperformance attributes which function to effectuate a closely conformingfit to the body of the wearer or to the frame of the item. It isdesirable to maintain the conforming fit during repeated use, extensionsand retractions at body temperatures. Further, for incontinencearticles, stretchability and elasticity are particularly desirable toensure comfort and provide security against unwanted leaks.

Disposable articles are typically elastic composite materials preparedfrom a combination of polymer film, fibers, sheets and absorbentmaterials as well as a combination of fabrication technologies. Whereasthe fibers are prepared by well known processes such as spun bonding,melt blowing, melt spinning and continuous filament wounding techniques,the film and sheet forming processes typically involve known extrusionand coextrusion techniques, e.g., blown film, cast film, profileextrusion, injection molding, extrusion coating, and extrusion sheeting.

A material is typically characterized as elastic where it has a highpercent elastic recovery (i.e., a low percent permanent set) afterapplication of a biasing force. Ideally, elastic materials arecharacterized by a combination of three important properties, i.e., alow percent permanent set, a low stress or load at strain, and a lowpercent stress or load relaxation. That is, there should be (1) a lowstress or load requirement to stretch the material, (2) no or lowrelaxing of the stress or unloading once the material is stretched, and(3) complete or high recovery to original dimensions after thestretching, biasing or straining is discontinued.

Lycra (spandex) is a segmented polyurethane elastic material which isknown to exhibit good elastic properties. But Lycra tends to beextremely cost prohibitive for a many of applications. Also, Lycra likenatural rubbers tend to exhibit poor environmental resistance to ozone,chlorine and high temperature, especially in the presence of moisture.

Natural rubbers, as discussed by Ferdinand Rodriguez in Principles ofPolymer Systems, pp. 242-43, McGraw-Hill (1982), the disclosure of whichis incorporated herein by reference, generally show decreases inelongation to break with increase in degree of crosslinking.Furthermore, at high degrees of crosslinking, even tenacity at break maydecrease for natural rubbers.

Elastic materials such as films, strips, coating, ribbons and sheetcomprising at least one substantially linear ethylene polymer aredisclosed in U.S. Pat. No. 5,472,775 to Obijeski et al., the disclosureof which is incorporated herein by reference. But U.S. Pat. No.5,472,775 does not disclose the performance of these materials atelevated temperatures (i.e., at temperatures above room temperature).

WO 94/25647 (Knight et al.), the disclosure of which is incorporatedherein by reference, discloses elastic fibers and fabrics made fromhomogeneously branched substantially linear ethylene polymers. Thefibers are said to posses at least 50 percent recovery (i.e., less thanor equal 50% permanent set) at 100 percent strain. But there is nodisclosure in WO 94/25647 regarding the elasticity of these fibers atelevated temperatures, nor is there any disclosure regarding resistanceto high temperatures.

U.S. Pat. No. 5,322,728 to Davey et al., the disclosure of which isincorporated herein by reference, discloses elastic fibers comprised ofsingle site catalyzed ethylene polymers. But polymers are not cured,irradiated or crosslinked and therefore are believed to exhibit poorelevated temperature elasticity.

WO 95/29197 (Penfold et al.), the disclosure of which is incorporatedherein by reference, discloses curable, silane-grafted substantiallyethylene polymers which are useful for use in wire and cable coatings,weather-stripping and fibers. WO 95/29197 reports examples which includefibers comprising silane-grafted substantially ethylene polymers havingdensities of 0.868 g/cm³ and 0.870 g/cm³. While example fibers are shownto exhibit improved elastic recovery at elevated temperatures, there isno disclosure regarding percent stress or load relaxation performance atelevated temperatures.

U.S. Pat. No. 5,324,576 to Reed et al., the disclosure of which isincorporated herein by reference, discloses an elastic nonwoven web ofmicrofibers of radiation crosslinked ethylene/alpha olefin copolymers,preferably having a density less than 0.9 g/cm³. The examples reportedin U.S. Pat. No. 5,324,576 comprise ethylene polymers having polymerdensities greater than or equal to 0.871 g/cm³ which subjected toelectron beam radiation. But Reed et al. provide no disclosure regardingthe elastic performance of these radiated polymers at elevatedtemperatures.

U.S. Pat. No. 5,525,257 to Kurtz et al., the disclosure of which isincorporated herein by reference, discloses that low levels ofirradiation of less than 2 megarads of Ziegler catalyzed linear lowdensity ethylene polymer results in improved stretchability and bubblestability without measurable gelation.

U.S. Pat. No. 4,425,393 to Benedyk et al., the disclosure of which isincorporated herein by reference, discloses low modulus fibers havingdiameters in the range of 0.5 to 3 mils (about 1 to about 37 denier).

Canadian Patent No. 935,598 to Hardy et al., the disclosure of which isincorporated herein by reference, discloses elastic fibers comprised ofvarious ethylene polymers wherein the fibers are post-drawn (stretched)and crosslinked while under tension.

U.S. Pat. No. 4,957,790 to Warren, the disclosure of which isincorporated herein by reference, discloses the use of pro-rad compoundsand irradiation to prepare heat-shrinkable linear low densitypolyethylene films having an increased orientation rate duringfabrication. In the examples provided therein, Warren employs Zieglercatalyzed ethylene polymers having densities greater than or equal to0.905 g/cm³.

In spite of various disclosures relating to elastic ethylene polymerarticles, including articles comprising curable, radiated and/orcrosslinked ethylene polymers, there is a present need forcost-effective elastic articles having good heat resistance andelasticity at elevated temperatures, especially at human bodytemperatures of about 100° F. There is also a need for a method ofmaking elastic articles having good elasticity at elevated temperatures.We have discovered that these and other objects can be completely met bythe invention herein described.

SUMMARY OF THE INVENTION

We have discovered that elastic articles comprising a substantiallycured, radiated or crosslinked ethylene polymer wherein the polymer ischaracterized as having a polymer density of less than 0.89 g/cm³,especially less than 0.87 g/cm³ and most especially less than or equalto 0.865 g/cm³ (or a differential scanning calorimetry (DSC)crystallinity at 23° C. of less than 26 weight percent, especially 12weight percent, and most especially less than or equal to 8.5 weightpercent). These novel articles exhibit excellent elasticity at roomtemperature and at elevated temperatures.

The broad aspect of the invention provides a heat resistant, shapedcured, irradiated or crosslinked article comprising an ethyleneinterpolymer of ethylene interpolymerized with at least one othermonomer and characterized as having:

a) a polymer density of less than 0.89 g/cm³ or a DSC crystallinity at23° C., as determined using differential scanning calorimetry, of lessthan 26 weight percent before being shaped, cured, irradiated orcrosslinked and

b) in meltspun fiber form, a value less than 0.75 for the expression

Abs[ΔE/E ₀ ]+Abs[ΔT/T ₀]

where ΔE and ΔT are taken from a stress-strain plot, as determined usingan Instron tensiometer at 500 mm/minute crosshead speed and 10.2 cm gagelength and from the average of four replications of five fiber samples;ΔE is taken as the difference in percent elongation between the cured,irradiated or crosslinked polymer and the uncured, irradiated oruncrosslinked interpolymer at a tenacity of 0.4 grams/denier; E₀ istaken as the percent elongation of the uncured, irradiated oruncrosslinked interpolymer at a tenacity of 0.4 grams/denier; ΔT istaken as the difference in tenacity (in grams/denier) between the cured,irradiated or crosslinked polymer and the uncured, irradiated oruncrosslinked polymer at a percent elongation of 300 percent; T₀ istaken as the tenacity (in grams/denier) of the uncured, irradiated oruncrosslinked interpolymer at a percent elongation of 300 percent; andAbs denotes absolute value.

Another aspect of the invention is a heat resistant cured, irradiated orcrosslinked elastic fiber comprising ethylene interpolymerized with atleast one other monomer wherein the interpolymer is characterized ashaving:

a) polymer density of less than 0.89 g/cm³ or a crystallinity at 23° C.,as determined using differential scanning calorimetry, of less than 26weight percent before being shaped, cured, irradiated or crosslinked and

b) in meltspun fiber form, a value less than 0.75 for the expression

Abs[ΔE/E ₀ ]+Abs[ΔT/T ₀]

where ΔE and ΔT are taken from a stress-strain plot, as determined usingan Instron tensiometer at 500 mm/minute crosshead speed and 10.2 cm gagelength and from the average of four replications of five fiber samples;ΔE is taken as the difference in percent elongation between the cured,irradiated or crosslinked polymer and the uncured, irradiated oruncrosslinked interpolymer at a tenacity of 0.4 grams/denier; E₀ istaken as the percent elongation of the uncured, irradiated oruncrosslinked interpolymer at a tenacity of 0.4 grams/denier; ΔT istaken as the difference in tenacity (in grams/denier) between the cured,irradiated or crosslinked polymer and the uncured, irradiated oruncrosslinked polymer at a percent elongation of 300 percent; T₀ istaken as the tenacity (in grams/denier) of the uncured, irradiated oruncrosslinked interpolymer at a percent elongation of 300 percent; andAbs denotes absolute value.

A third aspect of the invention is a heat resistant shaped elasticarticle which comprises at least one ethylene interpolymer which hasbeen cured, irradiated or crosslinked wherein the interpolymer comprisesethylene interpolymerized with at least one other monomer and ischaracterized as having:

(a) a polymer density of less than 0.87 g/cm³ before being shaped,cured, irradiated or crosslinked,

(b) a percent permanent set of less than or equal 25 at 23° C. and 200percent strain when measured at a 2 mil thickness using an Instrontensiometer after being shaped, cured, irradiated or crosslinked,

(c) a percent stress relaxation of less than or equal 25 at 23° C. and200 percent strain when measured at a 2 mil thickness using a Instrontensiometer after being shaped, cured, irradiated or crosslinked, and

(d) a percent stress relaxation of less than or equal 55 at 38° C. and200 percent strain when measured at a 2 mil thickness using an Instrontensiometer after.

A fourth aspect of the invention is a method of making an elasticarticle comprising the steps of

(a) providing an ethylene interpolymer having a density of less than0.87 g/cm³,

(b) fabricating the article from the interpolymer, and

(c) after the fabrication, subjecting the article to heat or ionizingradiation or both.

A fifth aspect of the invention is a method of making an elastic articlecomprising the steps of

(a) providing an ethylene interpolymer having a density of less than0.87 g/cm³,

(b) incorporating a pro-rad crosslink additive into the interpolymer,

(c) fabricating the article from the interpolymer, and

(d) after fabrication, subjecting the article to heat or ionizingradiation or both.

Preferably, the article is fabricated using an extrusion technique(i.e., the method consists of melting the interpolymer). Suitableextrusion techniques include, but are not limited to, fiber meltspinning, fiber melt blowing, film blowing, cast filed, injectionmolding, or rotomolding technique. Preferably, the extrudate, filament,web or part is permitted to cool or is quenched to ambient temperature(i.e., permitted to substantially solidify) before the application ofadditional heating or ionizing radiation.

In a preferred embodiment of the invention, the ethylene polymer is ahomogeneously branched ethylene polymer, especially a substantiallylinear ethylene polymer. In another preferred embodiment, the ionizingradiation is provided by electron beam irradiation.

We discovered that (unlike natural rubbers) curing, irradiation orcrosslinking (increased crosslink densities) do not decrease theelongation at break or tenacity at break for homogeneously branchedethylene polymers having a polymer density of less than 0.89 g/cm³ andthat articles (especially fibers) of cured, irradiated or crosslinkedhomogeneously branched ethylene polymers exhibit substantially improveheat resistance.

We also discovered that there is a subset of ethylene polymers whichprovide completely unexpected elastic performance results when cured,radiated or crosslinked. In particular, we found for the broad range ofpolymer densities above and below 0.87 g/cm³, curing, radiation orcrosslinking dramatically decrease percent permanent set performance(i.e., improve elasticity or elastic recovery) and have no substantialeffect on ambient percent stress or load relaxation performance. Butwhile tending to adversely affect (i.e., increase) or have no effect onpercent stress or load relaxation at elevated temperatures for polymerhaving densities equal to or greater than 0.865 g/cm³, surprisinglycuring, radiation and crosslinking decreases (i.e., improves) theelevated temperature percent stress or load relaxation performance ofethylene interpolymer having a polymer density less than 0.87 g/cm³ or aDSC crystallinity at 23° C. less than 12 weight percent. That is,curing, radiating or crosslinking is an effective means for providingelastic materials and articles characterized as having excellentelevated temperature stress relaxation characteristics.

Not only is the dramatically different response to irradiation orcrosslinking surprisingly in itself, these results are surprising forother reasons as well. For example, these results are surprising andunexpected because at a density of 0.87 g/cm³, ethylene polymers arealready substantially amorphous. That is, a cross-over or transition inelastic performance attributable to curing, radiation or crosslinkingwould ordinarily be expected to relate to the amorphosity of thepolymer; but according to hexane extraction data at 50° C., determinedaccording to the Food and Drug Administration (FDA) test method setforth under 21 37 C.F.R. §§177.1520 (d)(3)(ii), ethylene polymers aresubstantially amorphous at a density of 0.89 g/cm³ and below. Given suchsmall differences in amorphosity or crystallinity, dramatic elasticitydifferences in response to irradiation or crosslinking simply would notordinarily be expected.

Accordingly, the shaped elastic articles of present invention exhibit aunique combination of properties such as tenacity at break, elongation,elastic recovery, chlorine and aromatic/polar solvent resistance,moisture resistance, heat aging and excellent high temperaturemechanical performance compared to traditional elastic materials, forexample, natural rubber and spandex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of percent stress relaxation at 23° C. versus megaradsof electron beam radiation for Inventive Examples 1 and 2 andcomparative runs 3, 4 and 5.

FIG. 2 is a plot of percent permanent set at 23° C. versus megarads ofelectron beam radiation for Inventive Examples 1 and 2 and comparativeruns 3, 4 and 5.

FIG. 3 is a plot of percent stress relaxation at 38° C. versus megaradsof electron beam radiation for Inventive Example 1 and comparative run4.

FIG. 4 is a stress-strain comparison between Inventive Example 6 andcomparative run 7.

FIG. 5 is a plot of percent elastic recovery (as percent set elongation)versus percent elongation (strain) for Inventive Example 6.

DETAILED DESCRIPTION OF THE INVENTION

The term “elastic” as used herein refers to a material having apermanent set less than 60 percent, especially less than or equal to 25percent (i.e. especially greater than or equal to 87.5 percent recovery)at 200 percent strain and is stretchable to a stretched, biased lengthat least 150 percent greater than its relaxed, unstretched length.Elastic materials are also referred to in the art as “elastomers” and“elastomeric”.

The term “nonelastic” as used herein means the material or article isnot elastic as defined herein (i.e. the martial or article has a percentpermanent set greater than

Elastic materials and articles include, the cured, radiated orcrosslinked article, ethylene interpolymer itself or both as well as,but not limited to, a fiber, film, strip, tape, ribbon, sheet, coating,molding and the like comprised of the cured, radiated or crosslinkedethylene interpolymer. Preferred elastic articles are fiber and

The term “radiated” or “irradiated” as used herein means the ethylenepolymer, the shaped ethylene interpolymer or the article comprised ofthe ethylene polymer was subjected to at least 3 megarads (or theequivalent thereof) of radiation dose whether or not there was ameasurable decrease in percent xylene extractables (i.e., increase ininsoluble gel). That is, substantial crosslinking may not result fromthe irradiation.

The terms “crosslinked” and “substantially crosslinked” as used hereinmean the ethylene polymer, the shaped ethylene interpolymer or thearticle comprised of the ethylene polymer is characterized as havingxylene extractables of less than or equal to 70 weight percent (that is,greater than or equal to 30 weight percent gel content), preferablygreater than or equal to 40 weight percent (that is, greater than orequal to 60 weight percent gel content), where xylene extractables (andgel content) are determined in accordance with ASTM D-2765.

The terms “cured” and “substantially cured” as used herein means theethylene interpolymer, the shaped ethylene interpolymer or the articlecomprised of the ethylene interpolymer was subjected or exposed to atreatment which induced crosslinking. As used herein, the terms relateto ethylene interpolymers comprising a grafted silane.

The terms “curable” and “crosslinkable” as used herein mean the ethyleneinterpolymer, the shaped ethylene interpolymer or the article comprisedof the ethylene interpolymer is not crosslinked and has not beensubjected or exposed to treatment which induces crosslinking althoughthe ethylene interpolymer, the shaped ethylene interpolymer or thearticle comprised of the ethylene interpolymer comprises additive(s) orfunctionality which will effectuate crosslinking upon subjection orexposure to such treatment.

In the practice of the present invention, curing, irradiation orcrosslinking can be accomplished by any means known in the art,including, but not limited to, electron-beam irradiation, betairradiation, gamma irradiation, corona irradiation, peroxides, allylcompounds and UV radiation with or without crosslinking catalyst.Electron-beam irradiation is preferred.

Suitable electron-beam irradiation equipment is available from EnergyServices, Inc. Wilmington, Mass. with capabilities of at least 100 KeVand at least 5 Kw.

The term “pro-rad additive” as used herein means a compound which is notactivated during normal fabrication or processing of the ethyleneinterpolymer, however can be activated by the application oftemperatures (heat) substantial above normal fabrication or processingtemperatures or ionizing energy (or both) to effectuate some measurablegelation or preferably, substantial crosslinking.

The term “homofil” as used herein refers to fiber which has a singlepolymer region or domain and does not have any other distinct polymerregions (as do bicomponent fibers).

The term “meltblown” is used herein in the conventional sense to referto fibers formed by extruding a molten thermoplastic polymer compositionthrough a plurality of fine, usually circular, die capillaries as moltenthreads or filaments into converging high velocity gas streams (e.g.air) which function to attenuate the threads or filaments to reduceddiameters. Thereafter, the filaments or threads are carried by the highvelocity gas streams and deposited on a collecting surface to form a webof randomly dispersed meltblown fibers with average diameters generallysmaller than 10 microns.

The term “spunbond” is used herein in the conventional sense to refer tofibers formed by extruding a molten thermoplastic polymer composition asfilaments through a plurality of fine, usually circular, die capillariesof a spinneret with the diameter of the extruded filaments then beingrapidly reduced and thereafter depositing the filaments onto acollecting surface to form a web of randomly dispersed spunbond fiberswith average diameters generally between about 7 and about 30 microns.

The term “nonwoven” as used herein and in the conventional sense means aweb or fabric having a structure of individual fibers or threads whichare randomly interlaid, but not in an identifiable manner as is the casefor a knitted fabric. The elastic fiber of the present invention can beemployed to prepare nonwoven fabrics as well as composition structurescomprises elastic nonwoven fabric in combination with nonelasticmaterials.

The term “conjugated” refers to fibers which have been formed from atleast two polymers extruded from separate extruders but meltblown orspun together to form one fiber. Conjugated fibers are sometimesreferred to in the art as muticomponent or bicomponent fibers. Thepolymers are usually different from each other although conjugatedfibers may be monocomponent fibers. The polymers are arranged insubstantially constantly positioned distinct zones across thecross-section of the conjugated fibers and extend continuously along thelength of the conjugated fibers. The configuration of conjugated fiberscan be, for example, a sheath/core arrangement (wherein one polymer issurrounded by another), a side by side arrangement, a pie arrangement oran “islands-in-the sea” arrangement. Conjugated fibers are described inU.S. Pat. No. 5,108,820 to Kaneko et al.; U.S. Pat. No. 5,336,552 toStrack et al.; and U.S. Pat. No. 5,382,400 to Pike et al., thedisclosures of all of which are incorporated herein by reference. Theelastic fiber of the present invention can be in a conjugatedconfiguration, for example, as a core or sheath, or both.

The ethylene interpolymer to be irradiated, cured or crosslinked has adensity at 23° C. less than 0.89 g/cm³, preferably less than 0.87 g/cm³,more preferably less than or equal to 0.865 g/cm³, especially in therange of about 0.865 g/cm³ to about 0.355 g/cm³, as measured inaccordance with ASTM D792. At densities higher than 0.839 g/cm³ thedesired improved high temperature elastic performance (especially, lowpercent stress or load relaxation) is not obtained. Densities less thanabout 0.855 g/cm³ are not preferred due to their low tenacity, very lowmelting point and pre-crosslink handing problems (blocking andtackiness).

Preferably, the ethylene interpolymer is characterized as having a DSCcrystallinity of less than 26 weight percent, preferably less than 12weight percent, more preferably less than or equal to 8.5 weightpercent, and most preferably less than or equal 6 percent.

Preferably, the ethylene interpolymer is characterized as having a meltindex (I₂) less than 50, more preferably less than 10 g/10 minutes, asdetermined in accordance with ASTM D-1238, Condition 190° C./2.16kilogram (kg).

In meltspun fiber form, the irradiated, cured or crosslinked ethylenepolymer of the present invention generally has a value less than 0.75,preferably less than 0.6, more preferably less than 0.5 for theexpression:

Abs[ΔE/E ₀ ]+Abs[ΔT/T ₀]

The irradiated, cured or crosslinked ethylene polymer of the presentinvention (and articles made therefrom) is characterized as having apercent permanent set of less than 60 at 23° C., preferably less than orequal 25 at 23° C., more preferably less than or equal to 20 and mostpreferably less than or equal to 15 at 23° C. and 38° C. and 200 percentstrain when measured at a 2 mil thickness using an Instron tensiometer;or preferably a percent set elongation of less than or equal to 25, morepreferably 20, most preferably 15 at 23° C. and 100 percent strain.

The irradiated, cured or crosslinked ethylene polymer of the presentinvention (and articles made therefrom) is characterized as having apercent stress relaxation of less than or equal 25 at 23° C. and 200percent strain and less than or equal to 55, preferably less than orequal to 50, more preferably less than or equal to 30, most preferablyless than or equal to 20 at 38° C. and 200 percent strain when measuredat a 2 mil thickness using a Instron tensiometer.

Irradiation may be accomplished by the use of high energy, ionizingelectrons, ultra violet rays, X-rays, gamma rays, beta particles and thelike and combination thereof. Preferably, electrons are employed up to70 megarads dosages. The irradiation source can be any electron beamgenerator operating in a range of about 150 kilovolts to about 6megavolts with a power output capable of supplying the desired dosage.The voltage can be adjusted to appropriate levels which may be, forexample, 100,000, 300,000, 1,000,000 or 2,000,000 or 3,000,000 or6,000,000 or higher or lower. Many other apparati for irradiatingpolymeric materials are known in the art. The irradiation is usuallycarried out at a dosage between about 3 megarads to about 35 megarads,preferably between about 8 to about 20 megarads. Further, theirradiation can be carried out conveniently at room temperature,although higher and lower temperatures, for example 0° C. to about 60°C., may also be employed. Preferably, the irradiation is carried outafter shaping or fabrication of the article. Also, in a preferredembodiment, the ethylene interpolymer which has been incorporated with apro-rad additive is irradiated with electron beam radiation at about 8to about 20 megarads.

Crosslinking can be promoted with a crosslinking catalyst, and anycatalyst that will provide this function can be used. Suitable catalystsgenerally include organic bases, carboxylic acids, and organometalliccompounds including organic titanates and complexes or carboxylates oflead, cobalt, iron, nickel, zinc and tin. Dibutyltindilaurate,dioctyltinmaleate, dibutyltindiacetate, dibutyltindioctoate, stannousacetate, stannous octoate, lead naphthenate, zinc caprylate, cobaltnaphthenate; and the like. Tin carboxylate, especiallydibutyltindilaurate and dioctyltinmaleate, are particularly effectivefor this invention. The catalyst (or mixture of catalysts) is present ina catalytic amount, typically between about 0.015 and about 0.035 phr.

Representative pro-rad additives include, but are not limited to, azocompounds, organic peroxides and polyfunctional vinyl or allyl compoundssuch as, for example, triallyl cyanurate, triallyl isocyanurate,pentaerthritol tetramethacrylate, glutaraldehyde, ethylene glycoldimethacrylate, diallyl maleate, dipropargyl maleate, dipropargylmonoallyl cyanurate, dicumyl peroxide, di-tert-butyl peroxide, t-butylperbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate,methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane,lauryl peroxide, tert-butyl peracetate, azobisisobutyl nitrite and thelike and combination thereof. Preferred pro-rad additives for use in thepresent invention are compounds which have poly-functional (i.e. atleast two) moieties such as C═C, C═N or C═O.

At least one pro-rad additive can be introduced to the ethyleneinterpolymer by any method known in the art. However, preferably thepro-rad additive(s) is introduced via a masterbatch concentratecomprising the same or different base resin as the ethyleneinterpolymer. Preferably, the pro-rad additive concentration for themasterbatch is relatively high e.g., about 25 weight percent (based onthe total weight of the concentrate).

The at least one pro-rad additive is introduced to the ethylene polymerin any effective amount. Preferably, the at least one pro-rad additiveintroduction amount is from about 0.001 to about 5 weight percent, morepreferably from about 0.005 to about 2.5 weight percent and mostpreferably from about 0.015 to about 1 weight percent (based on thetotal weight of the ethylene interpolymer.

The term “polymer”, as used herein, refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differenttype. As used herein, generic term “polymer” embraces the terms“homopolymer,” “copolymer,” “terpolymer” as well as “interpolymer.”

The term “interpolymer”, as used herein refers to polymers prepared bythe polymerization of at least two different types of monomers. As usedherein the generic term “interpolymer” includes the term “copolymers”(which is usually employed to refer to polymers prepared from twodifferent monomers) as well as the term “terpolymers” (which is usuallyemployed to refer to polymers prepared from three different types ofmonomers).

The term “homogeneously branched ethylene polymer” is used herein in theconventional sense to refer to an ethylene interpolymer in which thecomonomer is randomly distributed within a given polymer molecule andwherein substantially all of the polymer molecules have the sameethylene to comonomer molar ratio. The term refers to an ethyleneinterpolymer that are manufactured using so-called homogeneous orsingle-site catalyst systems known in the art such Ziegler vanadium,hafnium and zirconium catalyst systems and metallocene catalyst systemse.g., a constrained geometry catalyst systems which is further describedherein below.

Homogeneously branched ethylene polymers for use in the presentinvention can be also described as having less than 15 weight percent,preferably less 10 weight percent, more preferably less than 5 and mostpreferably zero (0) weight percent of the polymer with a degree of shortchain branching less than or equal to 10 methyls/1000 carbons. That is,the polymer contains no measurable high density polymer fraction (e.g.,there is no fraction having a density of equal to or greater than 0.94g/cm³), as determined, for example, using a temperature rising elutionfractionation (TREF) technique and infrared or 13C nuclear magneticresonance (NMR) analysis.

Preferably, the homogeneously branched ethylene polymer is characterizedas having a narrow, essentially single melting TREF profile/curve andessentially lacking a measurable high density polymer portion, asdetermined using a temperature rising elution fractionation technique(abbreviated herein as “TREF”).

The composition distribution of an ethylene interpolymer can be readilydetermined from TREF as described, for example, by Wild et al., Journalof Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982), or in U.S.Pat. Nos. 4,798,081; 5,008,204; or by L. D. Cady, “The Role of ComonomerType and Distribution in LLDPE Product Performance,” SPE RegionalTechnical Conference, Quaker Square Hilton, Akron, Ohio, October 1-2,pp. 107-119 (1985), the disclosures of all which are incorporated hereinby reference.

The composition (monomer) distribution of the interpolymer can also bedetermined using ¹³C NMR analysis in accordance with techniquesdescribed in U.S. Pat. Nos. 5,292,845; 4,798,081; 5,089,321 and by J. C.Randall, Rev. Macromol. Chem. Phys., C29, pp. 201-317 (1989), thedisclosures of all of which are incorporated herein by reference.

In analytical temperature rising elution fractionation analysis (asdescribed in U.S. Pat. No. 4,798,081 and abbreviated herein as “ATREF”),the film or composition to be analyzed is dissolved in a suitable hotsolvent (e.g., trichlorobenzene) and allowed to crystallized in a columncontaining an inert support (stainless steel shot) by slowly reducingthe temperature. The column is equipped with both a refractive indexdetector and a differential viscometer (DV) detector. An ATREF-DVchromatogram curve is then generated by eluting the crystallized polymersample from the column by slowly increasing the temperature of theeluting solvent (trichlorobenzene). The ATREF curve is also frequentlycalled the short chain branching distribution (SCBD) or compositiondistribution (CD) curve, since it indicates how evenly the comonomer(e.g., octene) is distributed throughout the sample in that as elutiontemperature decreases, comonomer content increases. The refractive indexdetector provides the short chain distribution information and thedifferential viscometer detector provides an estimate of the viscosityaverage molecular weight. The composition distribution and othercompositional information can also be determined using crystallizationanalysis fractionation such as the CRYSTAF fractionalysis packageavailable commercially from PolymerChar, Valencia, Spain.

Preferred homogeneously branched ethylene polymers (such as, but notlimited to, substantially linear ethylene polymers) have a singlemelting peak between −30 and 150° C., as determined using differentialscanning calorimetry (DSC), as opposed to traditional Zieglerpolymerized heterogeneously branched ethylene polymers (e.g., LLDPE andULDPE or VLDPE) which have two or more melting points.

The single melting peak is determined using a differential scanningcalorimeter standardized with indium and deionized water. The methodinvolves about 5-7 mg sample sizes, a “first heat” to about 180° C.which is held for 4 minutes, a cool down at 10° C./min. to −30° C. whichis held for 3 minutes, and heat up at 10° C./min. to 150° C. to providea “second heat” heat flow vs. temperature curve from which the meltingpeak(s) is obtained. Total heat of fusion of the polymer is calculatedfrom the area under the curve.

The homogeneously branched ethylene polymers for use in the inventioncan be either a substantially linear ethylene polymer or a homogeneouslybranched linear ethylene polymer.

The term “linear” as used herein means that the ethylene polymer doesnot have long chain branching. That is, the polymer chains comprisingthe bulk linear ethylene polymer have an absence of long chainbranching, as in the case of traditional linear low density polyethylenepolymers or linear high density polyethylene polymers made using Zieglerpolymerization processes (e.g., U.S. Pat. No. 4,076,698 (Anderson etal.)), sometimes called heterogeneous polymers. The term “linear” doesnot refer to bulk high pressure branched polyethylene, ethylene/vinylacetate copolymers, or ethylene/vinyl alcohol copolymers which are knownto those skilled in the art to have numerous long chain branches.

The term “homogeneously branched linear ethylene polymer” refers topolymers having a narrow short chain branching distribution and anabsence of long chain branching. Such “linear” uniformly branched orhomogeneous polymers include those made as described in U.S. Pat. No.3,645,992 (Elston) and those made using so-called single site catalystsin a batch reactor having relatively high ethylene concentrations (asdescribed in U.S. Pat. No. 5,026,798 (Canich) or in U.S. Pat. No.5,055,438 (Canich)) or those made using constrained geometry catalystsin a batch reactor also having relatively high olefin concentrations (asdescribed in U.S. Pat. No. 5,064,802 (Stevens et al.) or in EP 0 416 815A2 (Stevens et al.)).

Typically, homogeneously branched linear ethylene polymers areethylene/α-olefin interpolymers, wherein the α-olefin is at least oneC₃-C₂₀ α-olefin (e.g., propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene and the like) and preferably theat least one C₃-C₂₀ α-olefin is 1-butene, 1-hexene or 1-octene. Mostpreferably, the ethylene/α-olefin interpolymer is a copolymer ofethylene and a C₃-C₂₀ α-olefin, and especially an ethylene/C₄-C₈α-olefin copolymer such as an ethylene/1-octene copolymer,ethylene/1-butene copolymer, ethylene/1-pentene copolymer orethylene/1-hexene copolymer.

Suitable homogeneously branched linear ethylene polymers for use in theinvention are sold under the designation of TAFMER by Mitsui ChemicalCorporation and under the designations of EXACT and EXCEED resins byExxon Chemical Company.

The term “substantially linear ethylene polymer” as used herein meansthat the bulk ethylene polymer is substituted, on average, with about0.01 long chain branches/1000 total carbons to about 3 long chainbranches/1000 total carbons (wherein “total carbons” includes bothbackbone and branch carbons). Preferred polymers are substituted withabout 0.01 long chain branches/1000 total carbons to about 1 long chainbranches/1000 total carbons, more preferably from about 0.05 long chainbranches/1000 total carbons to about 1 long chain branched/1000 totalcarbons, and especially from about 0.3 long chain branches/1000 totalcarbons to about 1 long chain branches/1000 total carbons.

As used herein, the term “backbone” refers to a discrete molecule, andthe term “polymer” or “bulk polymer” refers, in the conventional sense,to the polymer as formed in a reactor. For the polymer to be a“substantially linear ethylene polymer”, the polymer must have at leastenough molecules with long chain branching such that the average longchain branching in the bulk polymer is at least an average of from about0.01/1000 total carbons to about 3 long chain branches/1000 totalcarbons.

The term “bulk polymer” as used herein means the polymer which resultsfrom the polymerization process as a mixture of polymer molecules and,for substantially linear ethylene polymers, includes molecules having anabsence of long chain branching as well as molecules having long chainbranching. Thus a “bulk polymer” includes all molecules formed duringpolymerization. It is understood that, for the substantially linearpolymers, not all molecules have long chain branching, but a sufficientamount do such that the average long chain branching content of the bulkpolymer positively affects the melt rheology (i.e., the shear viscosityand melt fracture properties) as described herein below and elsewhere inthe literature.

Long chain branching (LCB) is defined herein as a chain length of atleast one (1) carbon less than the number of carbons in the comonomer,whereas short chain branching (SCB) is defined herein as a chain lengthof the same number of carbons in the residue of the comonomer after itis incorporated into the polymer molecule backbone. For example, asubstantially linear ethylene/1-octene polymer has backbones with longchain branches of at least seven (7) carbons in length, but it also hasshort chain branches of only six (6) carbons in length.

Long chain branching can be distinguished from short chain branching byusing ¹³C nuclear magnetic resonance (NMR) spectroscopy and to a limitedextent, e.g. for ethylene homopolymers, it can be quantified using themethod of Randall, (Rev. Macromol. Chem. Phys., C29 (2&3), p. 285-297(1989)), the disclosure of which is incorporated herein by reference.However as a practical matter, current ¹³C nuclear magnetic resonancespectroscopy cannot determine the length of a long chain branch inexcess of about six (6) carbon atoms and as such, this analyticaltechnique cannot distinguish between a seven (7) carbon branch and aseventy (70) carbon branch. The long chain branch can be as long asabout the same length as the length of the polymer backbone.

Although conventional 13C nuclear magnetic resonance spectroscopy cannotdetermine the length of a long chain branch in excess of six carbonatoms, there are other known techniques useful for quantifying ordetermining the presence of long chain branches in ethylene polymers,including ethylene/1-octene interpolymers. For example, U.S. Pat. No.4,500,648, incorporated herein by reference, teaches that long chainbranching frequency (LCB) can be represented by the equation LCE=b/M_(w)wherein b is the weight average number of long chain branches permolecule and M_(w) is the weight average molecular weight. The molecularweight averages and the long chain branching characteristics aredetermined by gel permeation chromatography and intrinsic viscositymethods, respectively.

Two other useful methods for quantifying or determining the presence oflong chain branches in ethylene polymers, including ethylene/1-octeneinterpolymers are gel permeation chromatography coupled with a low anglelaser light scattering detector (GPC-LALLS) and gel permeationchromatography coupled with a differential viscometer detector (GPC-DV).The use of these techniques for long chain branch detection and theunderlying theories have been well documented in the literature. See,e.g., Zimm, G. H. and Stockmayer, W. H., J. Chem. Phys. 17, 1301 (1949)and Rudin, A., Modern Methods of Polymer Characterization, John Wiley &Sons, New York (1991) pp. 103-112, the disclosures of both of which areincorporated by reference.

A. Willem degroot and P. Steve Chum, both of The Dow Chemical Company,at the Oct. 4, 1994 conference of the Federation of Analytical Chemistryand Spectroscopy Society (FACSS) in St. Louis, Mo., presented datademonstrating that GPC-DV is indeed a useful technique for quantifyingthe presence of long chain branches in substantially linear ethylenepolymers. In particular, deGroot and Chum found that the level of longchain branches in substantially linear ethylene homopolymer samplesmeasured using the Zimm-Stockmayer equation correlated well with thelevel of long chain branches measured using ¹³C NMR.

Further, deGroot and Chum found that the presence of octene does notchange the hydrodynamic volume of the polyethylene samples in solutionand, as such, one can account for the molecular weight increaseattributable to octene short chain branches by knowing the mole percentoctene in the sample. By deconvoluting the contribution to molecularweight increase attributable to 1-octene short chain branches, deGrootand Chum showed that GPC-DV may be used to quantify the level of longchain branches in substantially linear ethylene/octene copolymers.

DeGroot and Chum also showed that a plot of Log (I₂, melt index) as afunction of Log (GPC Weight Average Molecular Weight) as determined byGPC-DV illustrates that the long chain branching aspects (but not theextent of long branching) of substantially linear ethylene polymers arecomparable to that of high pressure, highly branched low densitypolyethylene (LDPE) and are clearly distinct from ethylene polymersproduced using Ziegler-type catalysts such as titanium complexes andordinary homogeneous catalysts such as hafnium and vanadium complexes.

For substantially linear ethylene polymers, the empirical effect of thepresence of long chain branching is manifested as enhanced rheologicalproperties which are quantified and expressed in terms of gas extrusionrheometry (GER) results and/or melt flow, I₁₀/I₂, increases.

The substantially linear ethylene polymers used in the present inventionare a unique class of compounds that are further defined in U.S. Pat.No. 5,272,236, application Ser. No. 07/776,130, filed Oct. 15, 1991;U.S. Pat. No. 5,278,272, application Ser. No. 07/939,281, filed Sep. 2,1992; and U.S. Pat. No. 5,665,800, application Ser. No. 08/730,766,filed Oct. 16, 1996, each of which is incorporated herein by reference.

Substantially linear ethylene polymers differ significantly from theclass of polymers conventionally known as homogeneously branched linearethylene polymers described above and, for example, by Elston in U.S.Pat. No. 3,645,992. As an important distinction, substantially linearethylene polymers do not have a linear polymer backbone in theconventional sense of the term “linear” as is the case for homogeneouslybranched linear ethylene polymers.

Substantially linear ethylene polymers also differ significantly fromthe class of polymers known conventionally as heterogeneously branchedtraditional Ziegler polymerized linear ethylene interpolymers (forexample, ultra low density polyethylene, linear low density polyethyleneor high density polyethylene made, for example, using the techniquedisclosed by Anderson et al. in U.S. Pat. No. 4,076,698, in thatsubstantially linear ethylene interpolymers are homogeneously branchedpolymers. Further, substantially linear ethylene polymers also differfrom the class of heterogeneously branched ethylene polymers in thatsubstantially linear ethylene polymers are characterized as essentiallylacking a measurable high density or crystalline polymer fraction asdetermined using a temperature rising elution fractionation technique.

The homogeneously branched substantially linear ethylene polymers foruse in the present invention is characterized as having

(a) melt flow ratio, I₁₀/I₂≧5.63,

(b) a molecular weight distribution, M_(w)/M_(n), as determined by gelpermeation chromatography and defined by the equation:

(M _(w) /M _(n))≦(I ₁₀ /I ₂)−4.63,

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂ and M_(w)/M_(n) within ten percent of the substantially linearethylene polymer and wherein the respective critical shear rates of thesubstantially linear ethylene polymer and the linear ethylene polymerare measured at the same melt temperature using a gas extrusionrheometer,

(d) a single differential scanning calorimetry, DSC, melting peakbetween −30° and 150° C., and

(e) a density less than or equal to 0.865 g/cm³.

Determination of the critical shear rate and critical shear stress inregards to melt fracture as well as other rheology properties such as“rheological processing index” (PI), is performed using a gas extrusionrheometer (GER). The gas extrusion rheometer is described by M. Shida,R. N. Shroff and L. V. Cancio in Polymer Engineering Science, Vol. 17,No. 11, p. 770 (1977) and in Rheometers for Molten Plastics by JohnDealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99, thedisclosures of both of which are incorporated herein by reference.

The processing index (PI) is measured at a temperature of 190° C., atnitrogen pressure of 2500 psig using a 0.0296 inch (752 micrometers)diameter (preferably a 0.0143 inch diameter die for high flow polymers,e.g. 50-100 I₂ melt index or greater), 20:1 L/D die having an entranceangle of 180°. The GER processing index is calculated in millipoiseunits from the following equation:

PI=2.15×10⁶ dyne/cm ²/(1000×shear rate),

where: 2.15×10⁶ dyne/cm² is the shear stress at 2500 psi, and the shearrate is the shear rate at the wall as represented by the followingequation:

32 Q′/(60 sec/min)(0.745)(Diameter×2.54 cm/in)³, where:

Q′ is the extrusion rate (gms/min),

0.745 is the melt density of polyethylene (gm/cm³), and

Diameter is the orifice diameter of the capillary (inches).

The PI is the apparent viscosity of a material measured at apparentshear stress of 2.15×10⁶ dyne/cm².

For substantially linear ethylene polymers, the PI is less than or equalto 70 percent of that of a conventional linear ethylene polymer havingan I₂, M_(w)/M_(n) and density each within ten percent of thesubstantially linear ethylene polymer.

An apparent shear stress vs. apparent shear rate plot is used toidentify the melt fracture phenomena over a range of nitrogen pressuresfrom 5250 to 500 psig using the die or GER test apparatus previouslydescribed. According to Ramamurthy in Journal of Rheology, 30(2),337-357, 1986, above a certain critical flow rate, the observedextrudate irregularities may be broadly classified into two main types:surface melt fracture and gross melt fracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular gloss to the more severe form of“sharkskin”. In this disclosure, the onset of surface melt fracture ischaracterized at the beginning of losing extrudate gloss at which thesurface roughness of extrudate can only be detected by 40×magnification. The critical shear rate at onset of surface melt fracturefor the substantially linear ethylene polymers is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a linear ethylene polymer having about the same I₂ andM_(w)/M_(n). Preferably, the critical shear stress at onset of surfacemelt fracture for the substantially linear ethylene polymers of theinvention is greater than about 2.8×10⁶ dyne/cm².

Gross melt fracture occurs at unsteady flow conditions and ranges indetail from regular (alternating rough and smooth, helical, etc.) torandom distortions. For commercial acceptability, (e.g., in blown filmproducts), surface defects should be minimal, if not absent. Thecritical shear rate at onset of surface melt fracture (OSMF) andcritical shear stress at onset of gross melt fracture (OGMF) will beused herein based on the changes of surface roughness and configurationsof the extrudates extruded by a GER. For the substantially linearethylene polymers used in the invention, the critical shear stress atonset of gross melt fracture is preferably greater than about 4×10⁶dyne/cm².

For the processing index determination and for the GER melt fracturedetermination, substantially linear ethylene polymers are tested withoutinorganic fillers and do not have more than 20 ppm aluminum catalystresidue. Preferably, however, for the processing index and melt fracturetests, substantially linear ethylene polymers do contain antioxidantssuch as phenols, hindered phenols, phosphites or phosphonites,preferably a combination of a phenol or hindered phenol and a phosphiteor a phosphonite.

The molecular weight distributions of ethylene polymers are determinedby gel permeation chromatography (GPC) on a Waters 150 C. hightemperature chromatographic unit equipped with a differentialrefractometer and three columns of mixed porosity. The columns aresupplied by Polymer Laboratories and are commonly packed with pore sizesof 10³, 10⁴, 10⁵ and 10⁶ Å. The solvent is 1,2,4-trichlorobenzene, fromwhich about 0.3 percent by weight solutions of the samples are preparedfor injection. The flow rate is about 1.0 milliliters/minute, unitoperating temperature is about 140° C. and the injection size is about100 microliters.

The molecular weight determination with respect to the polymer backboneis deduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience, Polymer Letters, Vol. 6, p. 621, 1968, the disclosure of whichis incorporated herein by reference) to derive the following equation:

M _(polyethylene) =a*(M _(polystyrene))^(b).

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: M_(j)=(Σw_(i)(M_(i) ^(j)))^(j). Where w_(i) is the weightfraction of the molecules with molecular weight M_(i) eluting from theGPC column in fraction i and j=1 when calculating M_(w) and j=−1 whencalculating M_(n).

For the at least one homogeneously branched ethylene polymer used in thepresent invention, the M_(w)/M_(n) is preferably less than 3.5, morepreferably less than 3.0, most preferably less than 2.5, and especiallyin the range of from about 1.5 to about 2.5 and most especially in therange from about 1.8 to about 2.3.

Substantially linear ethylene polymers are known to have excellentprocessability, despite having a relatively narrow molecular weightdistribution (that is, the M_(w)/M_(n) ratio is typically less thanabout 3.5). Surprisingly, unlike homogeneously and heterogeneouslybranched linear ethylene polymers, the melt flow ratio (I₁₀/I₂) ofsubstantially linear ethylene polymers can be varied essentiallyindependently of the molecular weight distribution, M_(w)/M_(n).Accordingly, especially when good extrusion processability is desired,the preferred ethylene polymer for use in the present invention is ahomogeneously branched substantially linear ethylene interpolymer.

Suitable constrained geometry catalysts for use manufacturingsubstantially linear ethylene polymers include constrained geometrycatalysts as disclosed in U.S. application Ser. No. 07/545,403, filedJul. 3, 1990pending; U.S. application Ser. No. 07/758,654, filed Sep.12, 1991 now U.S. Pat. No. 5,132,380 U.S. Pat. No. 5,064,802(application Ser. No. 07/547,728); U.S. Pat. No. 5,470,993 (applicationSer. No. 08/241,523); U.S. Pat. No. 5,453,410 (application Ser. No.08/108,693); U.S. Pat. No. 5,374,696 (application Ser. No. 08/08,003);U.S. Pat. No. 5,532,394 (application Ser. No. 08/295,768); U.S. Pat. No.5,494,874 (application Ser. No. 08/294,469); and U.S. Pat. No. 5,189,192(application Ser. No. 07/647,111), the teachings of all of which areincorporated herein by reference.

Suitable catalyst complexes may also be prepared according to theteachings of WO 93/08199, and the patents issuing therefrom, all ofwhich are incorporated herein by reference. Further, themonocyclopentadienyl transition metal olefin polymerization catalyststaught in U.S. Pat. No. 5,026,798, which is incorporated herein byreference, are also believed to be suitable for use in preparing thepolymers of the present invention, so long as the polymerizationconditions substantially conform to those described in U.S. Pat. Nos.5,272,236; 5,278,272 and 5,665,800, especially with strict attention tothe requirement of continuous polymerization. Such polymerizationmethods are also described in PCT/US 92/08812 (filed Oct. 15, 1992).

The foregoing catalysts may be further described as comprising a metalcoordination complex comprising a metal of groups 3-10 or the Lanthanideseries of the Periodic Table of the Elements and a delocalize β-bondedmoiety substituted with a constrain-inducing moiety, said complex havinga constrained geometry about the metal atom such that the angle at themetal between the centroid of the delocalized, substituted pi-bondedmoiety and the center of at least one remaining substituent is less thansuch angle in a similar complex containing a similar pi-bonded moietylacking in such constrain-inducing substituent, and provided furtherthat for such complexes comprising more than one delocalized,substituted pi-bonded moiety, only one thereof for each metal atom ofthe complex is a cyclic, delocalized, substituted pi-bonded moiety. Thecatalyst further comprises an activating cocatalyst.

Suitable cocatalysts for use herein include polymeric or oligomericaluminoxanes, especially methyl aluminoxane, as well as inert,compatible, noncoordinating, ion forming compounds. So-called modifiedmethyl aluminoxane (MMAO) is also suitable for use as a cocatalyst. Onetechnique for preparing such modified aluminoxane is disclosed in U.S.Pat. No. 5,041,584, the disclosure of which is incorporated herein byreference. Aluminoxanes can also be made as disclosed in U.S. Pat. Nos.5,218,071; 5,086,024; 5,041,585; 5,041,583; 5,015,749; 4,960,878; and4,544,762, the disclosures of all of which are incorporated herein byreference.

Aluminoxanes, including modified methyl aluminoxanes, when used in thepolymerization, are preferably used such that the catalyst residueremaining in the (finished) polymer is preferably in the range of fromabout 0 to about 20 ppm aluminum, especially from about 0 to about 10ppm aluminum, and more preferably from about 0 to about 5 ppm aluminum.In order to measure the bulk polymer properties (e.g. PI or meltfracture), aqueous HCL is used to extract the aluminoxane from thepolymer. Preferred cocatalysts, however, are inert, noncoordinating,boron compounds such as those described in EP 520732, the disclosure ofwhich is incorporated herein by reference.

Substantially linear ethylene are produced via a continuous (as opposedto a batch) controlled polymerization process using at least one reactor(e.g., as disclosed in WO 93/07187, WO 93/07188, and WO 93/07189, thedisclosure of each of which is incorporated herein by reference), butcan also be produced using multiple reactors (e.g., using a multiplereactor configuration as described in U.S. Pat. No. 3,914,342, thedisclosure of which is incorporated herein by reference) at apolymerization temperature and pressure sufficient to produce theinterpolymers having the desired properties. The multiple reactors canbe operated in series or in parallel, with at least one constrainedgeometry catalyst employed in at least one of the reactors.

Substantially linear ethylene polymers can be prepared via thecontinuous solution, slurry, or gas phase polymerization in the presenceof a constrained geometry catalyst, such as the method disclosed in EP416,815-A, the disclosure of which is incorporated herein by reference.The polymerization can generally be performed in any reactor systemknown in the art including, but not limited to, a tank reactor(s), asphere reactor(s), a recycling loop reactor(s) or combinations thereofand the like, any reactor or all reactors operated partially orcompletely adiabatically, nonadiabatically or a combination of both andthe like. Preferably, a continuous loop-reactor solution polymerizationprocess is used to manufacture the substantially linear ethylene polymerused in the present invention.

In general, the continuous polymerization required to manufacturesubstantially linear ethylene polymers may be accomplished at conditionswell known in the prior art for Ziegler-Natta or Kaminsky-Sinn typepolymerization reactions, that is, temperatures from 0 to 250° C. andpressures from atmospheric to 1000 atmospheres (100 MPa). Suspension,solution, slurry, gas phase or other process conditions may be employedif desired.

A support may be employed in the polymerization, but preferably thecatalysts are used in a homogeneous (i.e., soluble) manner. It will, ofcourse, be appreciated that the active catalyst system forms in situ ifthe catalyst and the cocatalyst components thereof are added directly tothe polymerization process and a suitable solvent or diluent, includingcondensed monomer, is used in said polymerization process. It is,however, preferred to form the active catalyst in a separate step in asuitable solvent prior to adding the same to the polymerization mixture.

The substantially linear ethylene polymers used in the present inventionare interpolymers of ethylene with at least one C₃-C₂₀ α-olefin and/orC₄-C₁₈ diolefin. Copolymers of ethylene and an α-olefin of C₃-C₂₀ carbonatoms are especially preferred. The term “interpolymer” as discussedabove is used herein to indicate a copolymer, or a terpolymer, or thelike, where, at least one other comonomer is polymerized with ethyleneor propylene to make the interpolymer.

Suitable unsaturated comonomers useful for polymerizing with ethyleneinclude, for example, ethylenically unsaturated monomers, conjugated ornon-conjugated dienes, polyenes, etc. Examples of such comonomersinclude C₃-C₂₀ α-olefins such as propylene, isobutylene, 1-butene,1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene,1-decene, and the like. Preferred comonomers include propylene,1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, and1-octene, and 1-octene is especially preferred. Other suitable monomersinclude styrene, halo- or alkyl-substituted styrenes,vinylbenzocyclobutane, 1,4-hexadiene, 1,7-octadiene, and naphthenics(e.g., cyclopentene, cyclohexene and cyclooctene).

The ethylene interpolymer can be blended with other polymers. Suitablepolymers for blending with the ethylene interpolymer are commerciallyavailable from a variety of suppliers and include, but are not limited,an ethylene polymer (e.g., low density polyethylene, ultra or very lowdensity polyethylene, medium density polyethylene, linear low densitypolyethylene, high density polyethylene, homogeneously branched linearethylene polymer, substantially linear ethylene polymer, polystyrene,ethylene styrene interpolymer, ethylene vinyl acetate interpolymer,ethylene acrylic acid interpolymer, ethylene ethyl acetate interpolymer,ethylene methacrylic acid interpolymer, ethylene methacrylic acidionomer, and the like), polycarbonate, polystyrene, polypropylene (e.g.,homopolymer polypropylene, polypropylene copolymer, random blockpolypropylene interpolymer and the like), thermoplastic polyurethane,polyamide, polylactic acid interpolymer, thermoplastic block polymer(e.g. styrene butadiene copolymer, styrene butadiene styrene triblockcopolymer, styrene ethylene-butylene styrene triblock copolymer and thelike), polyether block copolymer (e.g., PEBAX), copolyester polymer,polyester/polyether block polymers (e.g., HYTREL), ethylene carbonmonoxide interpolymer (e.g., ethylene/carbon monoxide (ECO), copolymer,ethylene/acrylic acid/carbon monoxide (EAACO) terpolymer,ethylene/methacrylic acid/carbon monoxide (EMAACO) terpolymer,ethylene/vinyl acetate/carbon monoxide (EVACO) terpolymer andstyrene/carbon monoxide (SCO)), polyethylene terephthalate (PET),chlorinated polyethylene, and the like and mixtures thereof.

In one preferred embodiment, the ethylene interpolymer is blended with apolypropylene resins. Suitable polypropylene polymers for use in theinvention, including random block propylene ethylene polymers, areavailable from a number of manufacturers, such as, for example, MontellPolyolefins and Exxon Chemical Company. At Exxon, suitable polypropylenepolymers are supplied under the designations ESCORENE and ACHIEVE.

Suitable poly lactic acid (PLA) polymers for use in the invention arewell known in the literature (e.g., see D. M. Bigg et al., “Effect ofCopolymer Ratio on the Crystallinity and Properties of Polylactic AcidCopolymers”, ANTEC '96, pp. 2028-2039; WO 90/01521; EP 0 515203A; and EP0 748846A2, the disclosures of each of which are incorporated herein byreference). Suitable poly lactic acid polymers are supplied commerciallyby Cargill Dow under the designation EcoPLA.

Suitable thermoplastic polyurethane for use in the invention arecommercially available from The Dow Chemical Company under thedesignation PELLATHANE.

Suitable polyolefin carbon monoxide interpolymers can be manufacturedusing well known high pressure free-radical polymerization methods.However, they may also be manufactured using traditional Ziegler-Nattacatalysis and even with the use of so-called homogeneous catalystsystems such as those described and referenced herein above.

Suitable free-radical initiated high pressure carbonyl-containingethylene polymers such as ethylene acrylic acid interpolymers can bemanufactured by any technique known in the art including the methodstaught by Thomson and Waples in U.S. Pat. No. 3,520,861 and by McKinneyet al. in U.S. Pat. Nos. 4,988,781; 4,599,392; and 5,384,373, thedisclosures of which are incorporated herein by reference.

Suitable ethylene vinyl acetate interpolymers for use in the inventionare commercially available from various suppliers, including ExxonChemical Company and Du Pont Chemical Company.

Suitable ethylene/alkyl acrylate interpolymers are commerciallyavailable from various suppliers. Suitable ethylene/acrylic acidinterpolymers are commercially available from The Dow Chemical Companyunder the designation PRIMACOR. Suitable ethylene/methacrylic acidinterpolymers are commercially available from Du Pont Chemical Companyunder the designation NUCREL.

Chlorinated polyethylene (CPE), especially chlorinated substantiallylinear ethylene polymers, can be prepared by chlorinating polyethylenein accordance with well known techniques. Preferably, chlorinatedpolyethylene comprises equal to or greater than 30 weight percentchlorine. Suitable chlorinated polyethylenes for use in the inventionare commercially supplied by The Dow Chemical Company under thedesignation TYRIN.

Additives e.g., Irgafos® 168 or Irganox® 1010 supplied by Ciba GeigyCorp., may be added to the ethylene polymer protect against undodegradation during shaping or fabrication operation and/or to bettercontrol the extent of grafting or crosslinking (i.e., inhibit excessivegelation). In-process additives, e.g. calcium stearate, water,fluoropolymers, etc., may also be used for purposes such as for thedeactivation of residual catalyst and/or improved processability.

The ethylene interpolymer can be filled or unfilled. If filled, then theamount of filler present should not exceed an amount that wouldadversely affect elevated temperature elasticity. Typically, the amountof filler present is between 20 and 80, preferably between 50 and 70,weight percent (wt percent) based on the total weight of theinterpolymer. Representative fillers include kaolin clay, magnesiumhydroxide, silica, calcium carbonate. In a preferred embodiment, inwhich a filler is present, the filler is coated with a material thatwill prevent or retard any tendency that the filler might otherwise haveto interfere with the crosslinking reactions. Stearic acid isillustrative of such a filler coating.

The elastic ethylene interpolymer and elastic article of the inventionhave utility in a variety of applications. Suitable applicationsinclude, for example, but are not limited to, disposable personalhygiene products (e.g. training pants, diapers, absorbent underpants,incontinence products, feminine hygiene items and the like); disposablegarments (e.g. industrial apparel, coveralls, head coverings,underpants, pants, shirts, gloves, socks and the like); infectioncontrol/clean room products (e.g. surgical gowns and drapes, face masks,head coverings, surgical caps and hood, shoe coverings, boot slippers,wound dressings, bandages, sterilization wraps, wipers, lab coats,coverall, pants, aprons, jackets, bedding items and sheets and the like)and sports apparel.

Various homofil fibers can be made from the elastic ethyleneinterpolymer of the present invention, including staple fibers, spunbondfibers or melt blown fibers (using, e.g., systems as disclosed in U.S.Pat. No. 4,340,563 (Appel et al.), U.S. Pat. No. 4,663,220 (Wisneski etal.), U.S. Pat. No. 4,668,566 (Braun), or U.S. Pat. No. 4,322,027(Reba), all of which are incorporated herein by reference), and gel spunfibers (e.g., the system disclosed in U.S. Pat. No. 4,413,110 (Kavesh etal.), incorporated herein by reference)). Staple fibers can be melt spun(i.e., they can be extruded into the final fiber diameter directlywithout additional drawing), or they can be melt spun into a higherdiameter and subsequently hot or cold drawn to the desired diameterusing conventional fiber drawing techniques.

Elastic staple fibers of the present invention herein can also be usedas bonding fibers, especially where the inventive elastic fibers have alower melting point than the surrounding matrix fibers. In a bondingfiber application, the bonding fiber is typically blended with othermatrix fibers and the entire structure is subjected to heat, where thebonding fiber melts and bonds the surrounding matrix fiber. Typicalmatrix fibers which benefit from use of the inventive elastic fibersdisclosed herein include, but are not limited to, poly(ethyleneterephthalate) fibers, cotton fibers, nylon fibers, polypropylenefibers, heterogeneously branched polyethylene fibers, homogeneouslybranched ethylene polymer fibers, linear polyethylene homopolymer fibersand the like and combinations thereof. The diameter of the matrix fibercan vary depending upon the end use application.

Bicomponent fibers can also be made from the novel homogeneouslybranched substantially linear ethylene polymers. Such bicomponent fibershave the elastic ethylene interpolymer of the present invention in atleast one portion of the fiber. For example, in a sheath/corebicomponent fiber (i.e., one in which the sheath concentricallysurrounds the core), the elastic ethylene interpolymer can be in eitherthe sheath or the core. Different elastic ethylene interpolymers of thepresent invention can also be used independently as the sheath and thecore in the same fiber, preferably where both components are elastic andespecially where the sheath component has a lower melting point than thecore component. Other types of bicomponent fibers are within the scopeof the invention as well, and include such structures as side-by-sideconjugated fibers (e.g., fibers having separate regions of polymers,wherein the elastic ethylene interpolymer of the present inventioncomprises at least a portion of the fiber's surface).

The shape of the fiber is not limited. For example, typical fiber has acircular cross-sectional shape, but sometimes fibers have differentshapes, such as a trilobal shape, or a flat (i.e., “ribbon” like) shape.The elastic fiber disclosed herein is not limited by the shape of thefiber.

The heat resistant elastic fiber of the present invention can be usedwith other fibers such as PET, Nylon, cotton, etc. to make elasticfabrics. As an added advantage, the heat (and moisture) resistance ofthe elastic fiber of present invention can enable polyester PET fibersto be dyed at ordinary PET dyeing conditions. The other commonly usedelastic fibers, especially spandex, can only be used at less severe PETdyeing conditions to prevent degradation of properties.

Fiber diameter can be measured and reported in a variety of fashions.Generally, fiber diameter is measured in denier per filament. Denier isa textile term which is defined as the grams of the fiber per 9000meters of that fiber's length. Monofilament generally refers to anextruded strand having a denier per filament greater than 15, usuallygreater than 30. Fine denier fiber generally refers to fiber having adenier of about 15 or less. Microdenier (aka microfiber) generallyrefers to fiber having a diameter not greater than about 100micrometers. For the inventive elastic fibers disclosed herein, thediameter can be widely varied, with little impact upon the fiber'selasticity. But the fiber denier can be adjusted to suit thecapabilities of the finished article and as such, would preferably be:from about 0.5 to about 30 denier/filament for melt blown; from about 1to about 30 denier/filament for spunbond; and from about 1 to about20,000 denier/filament for continuous wound filament. Nonetheless,preferably, the nominal denier is greater than 37, more preferablygreater than or equal to 55 and most preferably greater than or equal to65. These preference are due to the fact that typically durable apparelemploy fibers with deniers greater than or equal to about 40.

Fabrics made from the inventive elastic fibers disclosed herein includeboth woven and nonwoven fabrics. Nonwoven fabrics can be made variously,including spunlaced (or hydrodynamically entangled) fabrics as disclosedin U.S. Pat. No. 3,485,706 (Evans) and U.S. Pat. No. 4,939,016(Radwanski et al.), the disclosures of which are incorporated herein byreference; by carding and thermally bonding staple fibers; byspunbonding continuous fibers in one continuous operation; or by meltblowing fibers into fabric and subsequently calandering or thermallybonding the resultant web. These various nonwoven fabric manufacturingtechniques are well known to those skilled in the art and the disclosureis not limited to any particular method. Other structures made from suchfibers are also included within the scope of the invention, includinge.g., blends of these novel fibers with other fibers (e.g.,poly(ethylene terephthalate) (PET) or cotton).

Fabricated articles which can be made using the inventive elastic fibersand fabrics disclosed herein include elastic composite articles (e.g.,diapers) that have elastic portions. For example, elastic portions aretypically constructed into diaper waist band portions to prevent thediaper from falling and leg band portions to prevent leakage (as shownin U.S. Pat. No. 4,381,781 (Sciaraffa), the disclosure of which isincorporated herein by reference). Often, the elastic portions promotebetter form fitting and/or fastening systems for a good combination ofcomfort and reliability. The inventive elastic fibers and fabricsdisclosed herein can also produce structures which combine elasticitywith breathability. For example, the inventive elastic fibers, fabricsand/or films of the present invention many be incorporated into thestructures disclosed in U.S. Pat. No. 6,176,952, the disclosure of whichis incorporated herein by reference.

The inventive elastic fibers and fabrics disclosed herein can also beused in various structures as described in U.S. Pat. No. 2,957,512(Wade), the disclosure of which is incorporated herein by reference. Forexample, layer 50 of the structure described in U.S. Pat. No. '512(i.e., the elastic component) can be replaced with the inventive elasticfibers and fabrics, especially where flat, pleated, creped, crimped,etc., nonelastic materials are made into elastic structures. Attachmentof the inventive elastic fibers and/or fabric disclosed herein tononelastic fibers, fabrics or other structures can be done by meltbonding or with adhesives. Gathered or shirred elastic structures can beproduced from the inventive elastic fibers and/or fabrics disclosedherein and nonelastic components by pleating the non-elastic component(as described in U.S. Pat. No. '512) prior to attachment, pre-stretchingthe elastic component prior to attachment, or heat shrinking the elasticcomponent after attachment.

The inventive elastic fibers described herein also can be used in aspunlaced (or hydrodynamically entangled) process to make novelstructures. For example, U.S. Pat. No. 4,801,482 (Goggans), thedisclosure of which is incorporated herein by reference, discloses anelastic sheet (12) which can now be made with the novel elasticfibers/fabric described herein.

Continuous elastic filaments as described herein could also be used inwoven applications where high resilience is desired.

The inventive elastic fibers and fabrics disclosed herein with adjust inthe interpolymer melt index and/or degree of crosslinking or extent orradiation also have adjustable tenacity and retractive force. Suchcapabilities and characteristics enable extensive design flexibility,for example, to provide for variable retractive force in the samegarment, if needed, as described for example in U.S. Pat. No. 5,196,000(Clear et al.), the disclosure of which is incorporated herein byreference.

U.S. Pat. No. 5,037,416 (Allen et al.), the disclosure of which isincorporated herein by reference, describes the advantages of a formfitting top sheet by using elastic ribbons (see member 19 of U.S. Pat.No. '416). The inventive elastic fibers could serve the function ofmember 19 of U.S. Pat. No. '416, or could be used in fabric form toprovide the desired elasticity.

Composites that utilize very high molecular weight linear polyethyleneor copolymer polyethylene also benefit from the inventive elastic fibersdisclosed herein. For example, the inventive elastic fibers have a lowmelting point (with the melting point of the polymer essentiallylinearly related to the polymer density), such that in a blend ofinventive elastic fibers disclosed herein and very high molecular weightpolyethylene fibers (e.g., Spectra™ fibers made by Allied Chemical) asdescribed in U.S. Pat. No. 4,584,347 (Harpell et al.), the disclosure ofwhich is incorporated herein by reference, the lower melting elasticfibers bond the high molecular weight polyethylene fibers withoutmelting the high molecular weight fibers, thus preserving the highstrength and integrity of the high molecular weight fiber.

In U.S. Pat. No. 4,981,747 (Morman), the inventive elastic fibers and/orfabrics disclosed herein can be substituted for elastic sheet 122, whichforms a composite elastic material including a reversibly neckedmaterial.

The inventive elastic fibers disclosed herein can also be a melt blownelastic component, as described in reference 6 of the drawings of U.S.Pat. No. 4,879,170 (Radwanski), the disclosure of which is incorporatedherein by reference. U.S. Pat. No. '170 generally describes elasticco-form material and manufacturing processes.

Elastic panels can also be made from the inventive elastic fibers andfabrics disclosed herein, and can be used, for example, as members 18,20, 14, and/or 26 of U.S. Pat. No. 4,940,464 (Van Gompel), thedisclosure of which is incorporated herein by reference. The inventiveelastic fibers and fabrics described herein can also be used as elasticcomponents of composite side panels (e.g., layer 86 of U.S. Pat. No.'464).

The elastic ethylene polymer can also be shaped or fabricated intoelastic films, coatings, sheets, strips, tapes, ribbons and the like.The elastic film, coating and sheet of the present invention may befabricated by any method known in the art, including blown bubbleprocesses (e.g., simple bubble as well as biaxial orientation techniquessuch trapped bubble, double bubble and tenter framing), cast extrusion,injection molding processes, thermoforming processes, extrusion coatingprocesses, profile extrusion, and sheet extrusion processes. Simpleblown bubble film processes are described, for example, in TheEncyclopedia of Chemical Technology, Kirk-Othmer, Third Edition, JohnWiley & Sons, New York, 1981, Vol. 16, pp. 416417 and Vol. 18, pp.191-192. The cast extrusion method is described, for example, in ModernPlastics Mid-October 1989 Encyclopedia Issue, Volume 66, Number 11,pages 256 to 257. Injection molding, thermoforming, extrusion coating,profile extrusion, and sheet extrusion processes are described, forexample, in Plastics Materials and Processes, Seymour S. Schwartz andSidney H. Goodman, Van Nostrand Reinhold Company, New York, 1982, pp.527-563, pp. 632-647, and pp. 596-602.

The elastic strips, tapes and ribbons of the present invention can beprepared by any known method, including the direct extrusion processingor by post-extrusion slitting, cutting or stamping techniques. Profileextrusion is an example of a primary extrusion process that isparticularly suited to the preparation of tapes, bands, ribbons and thelike.

The elastic materials of the present invention can also be renderedpervious or “breathable” by any method well known in the art includingby apperturing, slitting, microperforating, mixing with fibers or foams,incorporating fillers and stretching or combinations thereof. Examplesof such methods include, U.S. Pat. No. 3,156,242 by Crowe, Jr., U.S.Pat. No. 3,881,489 by Hartwell, U.S. Pat. No. 3,989,867 by Sisson andU.S. Pat. No. 5,085,654 by Buell, the disclosures of all of which areincorporate herein by reference.

Fabricated articles which can be made using the inventive elasticarticles disclosed herein include composite fabric articles (e.g.,disposable incontinence garments and diapers) that are comprised of oneor more elastic component or portion. The inventive elastic articlesdisclosed herein can also produce fabric composite structures whichcombine elasticity with breathability by utilizing a technique thatrenders the elastic material pervious or “breathable” such as suggestedby Lippert et al. in U.S. Pat. No. 4,861,652 and indicated above.

The inventive elastic articles disclosed herein can also be used invarious structures as described in U.S. Pat. No. 2,957,512 (Wade), thedisclosure of which is incorporated herein by reference. For example,layer 50 of the structure described in U.S. Pat. No. '512 (i.e., theelastic component) can be replaced with the novel elastic materials,especially where flat, pleated, creped, etc., nonelastic materials aremade into elastic or semi-elastic structures. Attachment of the novelelastic materials to nonelastic or less-elastic materials can be donewith heat bonding or with adhesives. Gathered or shirred elasticcomposite materials can be produced from the new elastic materialdescribed herein and nonelastic components by pleating the non-elasticcomponent (as described in U.S. Pat. No. '512) prior to attachment,prestretching the elastic component prior to attachment, or heatshrinking the elastic component after attachment.

The recovery after heat shrinking can be further enhanced byeffectuating a high degree of orientation into the inventive elasticarticles during fabrication. Significant orientation can be accomplishedby the utilization of various known techniques such as high blow-upblown film fabrication, tenter framing of cast films and “double bubble”or “trapped bubble” blown film fabrication.

The inventive elastic articles described herein can also be used makeother novel structures. For example, U.S. Pat. No. 4,801,482 (Goggans),the disclosure of which is incorporated herein by reference, disclosesan elastic sheet (12) which can now be made with the inventive elasticarticles described herein.

The inventive elastic articles described herein can also be used to makebreathable portion or breathable elastic composite materials. Forexample, U.S. Pat. No. 5,085,654 (Buell) discloses a leg band (15) witha breathable portion 45, a breathable topsheet (26), a breathablebacksheet (25), elastic elements (31 and 64), a breathable element (54),and a breathable sub-element (96) all or any combination of which cannow be made with the inventive elastic articles disclosed herein ineither pervious or impervious forms.

U.S. Pat. No. 5,037,416 (Allen et al.), the disclosure of which isincorporated herein by reference, describes the advantages of a formfitting top sheet by using elastic ribbons (member 12) and an elasticbacksheet (member 16). Pervious inventive elastic articles describedherein could serve the function of member 12 and impervious elasticsmaterials of this invention could function as member 16, or disclosedelastic materials could be used in an elastic composite fabric form.

In U.S. Pat. No. 4,981,747 (Morman), the inventive elastic articlesdisclosed herein can be substituted for elastic sheets 12, 122 and 232to construct an elastic composite material which includes a reversiblynecked material.

Elastic panels, elements, portions or the like can also be made from theinventive elastic articles disclosed herein, and can be used, forexample, as members 18, 20, 24, and/or 26 of U.S. Pat. No. 4,940,464(Van Gompel), the disclosure of which is incorporated herein byreference. The inventive elastic articles described herein can also beused, for example, as elastic composite side panels (e.g., layer) or aselastic ribbons 42 and/or 44.

The following examples are provided to further illustrate and illuminatethe present invention but are not intended to limit the invention to thespecific embodiments set forth.

EXAMPLES

In an evaluation to determine the elastic performance of variousethylene polymers in response to irradiation or crosslinking, fivedifferent ethylene interpolymers were subjected to varying degrees ofelectron beam radiation and their elastic properties as 2 mil cast filmswere measured at room temperature. The polymer densities and the meltindexes of the ethylene polymers are shown in Table 1. All of thepolymers were homogeneously branched ethylene/1-octene interpolymerssupplied commercially by Dupont Dow Elastomers, Ltd. and manufacturedusing a constrained geometry catalyst system. However, DDE 8190 alsocontained via blending 4-5 weight percent polypropylene. The densitiesfor the various polymer were determined in accordance with ASTM D-792and the melt indexes were determined in accordance with ASTM D-1238Condition 190° C./2.16 kilograms.

TABLE 1 Density Melt Index Polymer (g/cm³) (g/10 minutes) Designation A0.863 0.5 ENGAGE EG 8180 B 0.859 1.0 DDE 8190 C 0.870 1.0 ENGAGE EG 8100D 0.870 5.0 ENGAGE EG 8200 E 0.870 10 XU-58380.00

2 mil cast films of each polymer listed in Table 1 were fabricated usingconventional cast film extrusion equipment at melt temperatures of430°-500° F. After film fabrication, the cast films were electron beamradiated at various dosage using equipment similar to that described inU.S. Pat. No. 5,324,576, the disclosure of which is incorporated hereinby reference. The elastic properties (stress-strain dala) for thevarious films was determined using an Instron tensiometer set at 10inch/minute, except as otherwise indicated.

For the permanent set determinations at 23° C., the gage length was 2inches and the crosshead speed was 10 inches/minute. The test consistedof pulling the film sample to 200% strain (elongation) and holding itfor 30 seconds, then returning the crosshead to the starting point andholding it for 60 seconds, and then pulling the sample to determine thepoint where the load initially rises above zero. The percent permanentset was taken as the percent strain at which the load rose above zero.The test was a one cycle test which was run in duplicate.

For percent stress or load relaxation determination at 23° C., the gagelength was 2 inches and the crosshead speed was 10 inches/minute. Thistest consisted of pulling the film sample to 200% strain (elongation)and holding it for 30 seconds. The stress at initially at 200% strainwas taken as the maximum stress and the stress after the 30 secondholding period was taken as the minimum stress. The percent stress orload relaxation was run in duplicate and was calculated from thefollowing equation:$\frac{{{maximum}\quad {stress}} - {{minimum}\quad {stress}}}{{maximum}\quad {stress}} \times 100.$

Table 2 reports the elastic property (stress-strain) data as as thepermanent set and stress relaxation data for the various film samples.

Data in Table 2 was plotted and shown in FIGS. 1 and 2. FIG. 1 indicatesthat electron beam radiation up to 8-12 megarads has no substantialaffect on the percent stress relaxation performance of the variouspolymers. Conversely, FIG. 2 shows that irradiation has a dramaticaffect on the percent permanent set performance of the ethylenepolymers. However, FIG. 2 (like FIG. 1 and the results shown in WO95/29197) shows no particular distinction between the various polymersas the polymer density dominated the percent permanent set response andradiation affected the various polymer equally.

In another evaluation, 2 mil cast films of Resin A and Resin D weresubjected to varying dosages of electron beam radiation and evaluated todetermine their respective percent stress or load relaxationperformances at 38° C. This test was performed as described above,except the temperature was 38° C. instead of 23° C. and the sample washeld at 200% strain for 1 hour instead for 30 seconds. Table 3 shows theresults for this evaluation and FIG. 3 plots the results using theaverage of duplicative samples as well as a four-datapoint average forResin D at 5 and 8 megarads of electron beam radiation.

TABLE 2 * Inventive Ex. 1 * Inventive Ex. 2 Comparative Ex. 3* Resin A AA A B B B B C C C C e-Beam, megarad 0 3 5 8 0 3 5 8 0 3 5 8 100% StrainLoad 232 242 254 259 191 170 211 214 330 315 318 327 g/inch 200% StrainLoad, 269 290 318 354 226 211 235 238 409 384 380 395 g/inch % Strain @Break 762 651 785 491 1109 896 973 860 667 676 697 410 % Permanent Set21 9 10 22 17 11 7.5 6.6 41 28 20 23 @ 200% Strain % Stress 19 18 16 1920 17 19 20 22 20 25 21 Relaxation @ 200% Strain % Xylene NA 98.7 91.0468.2 NA 99.6 99.1 99.6 NA 99.6 99.8 73.9 Extractive Comparative Ex. 4*Comparative Ex. 5* Resin D D D D E E E E e-Beam, megarad 0 5 8 12 0 5 812 100% Strain Load 331 328 329 397 327 325 303 317 g/inch 200% StrainLoad, 387 357 423 379 367 430 382 385 g/inch % Strain @ Break 812 780883 784 909 869 809 773 % Permanent Set 42 24 35 22 50 24 24 26 @ 200%Strain % Stress 23 18 23 19 23 23 22 21 Relaxation @ 200% Strain %Xylene NA 99 7 99.3 81.5 NA 99 6 99.4 77.5 Extractive *not an example ofthe invention; provided for comparative purposes only.

TABLE 3 E-Beam Maximum Minimum % Stress megarads Stress, psi Stress, psiRelaxation Resin D (Comp. Ex. 4)  0 192 127 33.9  0 181 125 30.9  5 235112 52.3  5 230 108 53.0  8 231 132 42.9  8 245 136 44.5 12 250 120 52.012 227 115 49.3 Resin A (Inv. Ex. 1)  0 126 55 56.3  0 120 53 55.8  3120 57 52.5  3 134 59 56.0  5 134 64 52.2  5 142 69 51.4  8 137 70 48.9 8 145 78 46.2

The data in Table 3 and FIG. 3 show surprisingly the irradiation cansubstantially reduce the elevated temperature percent stress relaxationperformance of ethylene interpolymers having densities less than 0.87g/cm³ and conversely, show irradiation has no effect or increase theelevated temperature stress relaxation performance of ethyleneinterpolymers characterized as having densities greater than 0.87 g/cm³.The data in Table 3 also show that the minimum stress of ethyleneinterpolymers characterized as having densities less than 0.87 g/cm³desirably increases at higher dosage level. Extrapolation of FIG. 3indicates that at an electron beam radiation dosage level of about 20megarads, such interpolymer will exhibit a percent stress relaxation at38° C. of less than 20.

In another evaluation, a homogeneously branched ethylene polymer wasevaluated to determine its elongation-tenacity stability uponcrosslinking. The homogeneously branched ethylene polymer selected forthis evaluation was a substantially linear ethylene/1-octeneinterpolymer supplied by The Dow Chemical Company under the designationAFFINITY™ EG8200. This interpolymer has 512 melt index and a 0.87 g/ccdensity. The interpolymer also contained 200 ppm IRGANOX™ 1010, 2000 ppmChimassorb 944 (both supplied by Ciba-Geigy Corporation) and 800 ppmStandostab PEPQ™ (supplied by Sandox Chemicals). The polymer wasmeltspun into monofilament fibers of nominal 70-75 denier at Alex-JamesCorporation and wound onto spools. Subsequently, some of the spools wereelectron-beam irradiated at 32 Mrad dosage. The stress-strain properties(tenacity and percent elongation) of both crosslinked fibers (InventiveExample 6) and uncrosslinked fibers (comparative run 7) are shown in theFIG. 4.

FIG. 4 shows surprisingly the tenacity at break and percent elongationat break for Inventive Example 6 was not substantially reduced as aresult of a high degree of crosslinking (about 60-65 percent weight gelcontent). For the expression

Abs[ΔE/E ₀ ]+Abs[ΔT/T ₀]

Inventive Example 6 had a value of 0.46.

FIG. 5 which shows the elastic recovery (percent permanent set) resultsfor Inventive Example 6 indicates this fiber exhibited adequate elasticrecovery at percent elongations less than 100 percent as it would beused in a fabric form.

In another evaluation, the heat resistance of fibers was evaluated byexposing the fibers to elevated temperatures in a strained state. Thistest determines the survival probability of fibers subject to heatsetting and ironing. Because fiber in the fabric is in extended state,this test was conducted with fibers were tested in strained form.

Two strains, 50 percent and 300 percent, were used in the test. Theexposure to heat was 1 min, hence the test measures resistance to heatshock. Fibers were stretched to the desired extension in a lab stretcherand exposed to heat by inserting the stretcher in atemperature-equilibrated forced-air oven for 1 minute. The oventemperature was increased at 5° C. increments using new samples for eachtest until fiber fracture occurred for at least two repeats. Thetemperature where fracture occurred was recorded for each strain.

In this test, the heat resistance for comparative run 7 fiber was about80° C. at 50 percent elongation and 70° C. at 300 percent elongation.Conversely, the heat resistance of Inventive Example 6 was dramaticallyimproved. That is, for Inventive Example 6, the heat resistance wasgreater than 250° C. at both 50 percent and 300 percent elongation.

We claim:
 1. A heat-resistant, shaped, irradiated and crosslinkedarticle free of a silane crosslinker, and comprising an ethyleneinterpolymer of ethylene interpolymerized with at least one othermonomer and characterized as having: a) an interpolymer density of lessthan 0.89 g/cm³ or a DSC crystallinity at 23° C., as determined usingdifferential scanning calorimetry, of less than about 26 weight percentbefore being shaped, irradiated and crosslinked, b) xylene extractablesof less than or equal to about 70 weight percent and wherein the articleis in the form of a film.
 2. A heat-resistant, shaped and elasticarticle free of a silane crosslinkcr and which comprises at least oneethylene interpolymer which has been irradiated and crosslinked whereinthe interpolymer comprises ethylene interpolymerized with at least oneother monomer and is characterized as having: (a) an interpolymerdensity of less than or equal to 0.89 g/cm³ or a DSC crystallinity at23° C., as determined using differential scanning calorimetry, of lessthan about 26 weight percent before being shaped, irradiated andcrosslinked, (b) a percent permanent set of less than 60 at 23° C. and200 percent strain when measured at a 2 mil thickness using an Instrontensiometer after being shaped, irradiated and crosslinked, (c) apercent stress relaxation of less than or equal 25 at 23° C. and 200percent strain when measured at a 2 mil thickness using a Instrontensiometer after being shaped, irradiated and crosslinked, (d) apercent stress relaxation of less than or equal 55 at 38° C. and 200percent strain when measured at a 2 mil thickness using an Instrontensiometer after being shaped, irradiated and crosslinked, and whereinthe article is in the form of a film.
 3. A heat-resistant, shaped,irradiated and crosslinked article free of a silane crosslinker, andcomprising an ethylene interpolymer of ethylene interpolymerized with atleast one other monomer and characterized as having: a) an interpolymerdensity of less than 0.89 g/cm³ or a DSC crystallinity at 23° C., asdetermined using differential scanning calorimetry, of less than about26 weight percent before being shaped, irradiated and crosslinked, b)xylene extractables of less than or equal to about 70 weight percent,and wherein the article is in the form of a molding.
 4. Aheat-resistant, shaped and elastic article free of a silane crosslinkerand which comprises at least one ethylene interpolymer which has beenirradiated and crosslinked wherein the interpolymer comprises ethyleneinterpolymerized with at least one other monomer and is characterized ashaving: (a) an interpolymer density of less than or equal to 0.89 g/cm³or a DSC crystallinity at 23° C., as determined using differentialscanning calorimetry, of less than about 26 weight percent before beingshaped, irradiated and crosslinked, (b) a percent permanent set of lessthan 60 at 23° C. and 200 percent swain when measured at a 2 milthickness using an Instron tensiometer after being shaped, irradiatedand crosslinked, (c) a percent stress relaxation of less than or equal25 at 23° C. and 200 percent strain when measured at a 2 mil thicknessusing a Instron tensiometer after being shaped, irradiated andcrosslinked, (d) a percent stress relaxation of less than or equal 55 at38° C. and 200 percent strain when measured at a 2 mil thickness usingan Instron tensiometer alter being shaped, irradiated and crosslinked,and wherein the article is in the form of a molding.
 5. Aheat-resistant, shaped, irradiated and crosslinked article free of asilane crosslinker, and comprising an ethylene interpolymer of ethyleneinterpolymerized with at least one other monomer and characterized ashaving: a) an interpolymer density of less than 0.89 g/cm³ or a DSCcrystallinity at 23° C., as determined using differential scanningcalorimetry, of less than about 26 weight percent before being shaped,irradiated and crosslinked, b) xylene extractables of less than or equalto about 70 weight percent, and wherein the article is in the form of athermoform.
 6. A heat-resistant shaped and elastic article free of asilane crosslinker and which comprises at least one ethyleneinterpolymer which has been irradiated and crosslinked wherein theinterpolymer comprises ethylene interpolymerized with at least one othermonomer and is characterized as having: (a) an interpolymer density ofless than or equal to 0.89 g/cm³ or a DSC crystallinity at 23° C., asdetermined using differential scanning calorimetry, of less than about26 weight percent before being shaped irradiated and crosslinked, (b) apercent permanent set of less than 60 at 23° C. and 200 percent strainwhen measured at a 2 mil thickness using an Instron tensiometer afterbeing shaped, irradiated and crosslinked, (c) a percent stressrelaxation of less than or equal 25 at 23° C. and 200 percent strainwhen measured at a 2 mil thickness using a Instron tensiometer afterbeing shaped, irradiated and crosslinked, (d) a percent stressrelaxation of less than or equal 55 at 38° C. and 200 percent strainwhen measured at a 2 mil thickness using an Instron tensiometer afterbeing shaped, irradiated and crosslinked, and wherein die article is inthe form of a thermoform.
 7. A heat-resistant, shaped, irradiated andcrosslinked article free of a silane crosslinker, and comprising anethylene interpolymer of ethylene interpolymerized with at least oneother monomer and characterized as having: a) an interpolymer density ofless than 0.89 g/cm³ or a DSC crystallinity at 23° C., as determinedusing differential scanning calorimetry, of less than about 26 weightpercent before being shaped, irradiated and crosslinked, b) xyleneextractables of less than or equal to about 70 weight percent andwherein the article is in the form of a personal hygiene item.
 8. Theitem of claim 7 wherein the item is a disposable diaper.
 9. The item ofclaim 8 wherein the diaper comprises a backsheet or a topsheet comprisedof the shaped interpolymer.
 10. A heat-resistant, shaped and elasticarticle free of a silane crosslinker and which comprises at least oneethylene interpolymer which has been irradiated and crosslinked whereinthe interpolymer comprises ethylene interpolymerized with at least oneother monomer and is characterized as having: (a) an interpolymerdensity of less than or equal to 0.89 g/cm³ or a DSC crystallinity at23° C., as determined using differential scanning calorimetry, of lessthan about 26 weight percent before being shaped, irradiated andcrosslinked, (b) a percent permanent set of less than 60 at 23° C. and200 percent strain when measured at a 2 mil thickness using an matrontensiometer after being shaped, irradiated and crosslinked, (c) apercent stress relaxation of less than or equal 25 at 23° C. and 200percent strain when measured at a 2 mil thickness using a Instrontensiometer after being shaped, irradiated and crosslinked, (d) apercent stress relaxation of less than or equal 55 at 38° C. and 200percent stain when measured at a 2 mil thickness using an Instrontensiometer after being shaped, irradiated and crosslinked, and whereinthe article is in the form of a personal hygiene item.
 11. The item ofclaim 10 wherein the item is a disposable diaper.
 12. The item of claim11 wherein the diaper comprises a backsheet or a topsheet comprised ofthe shaped interpolymer.
 13. A heat-resistant, shaped, irradiated andcrosslinked article free of a silane crosslinker, and comprising anethylene interpolymer of ethylene interpolymerized with at least oneother monomer and characterized as having: a) an interpolymer density ofless than 0.89 g/cm³ or a DSC crystallinity at 23° C., as determinedusing differential scanning calorimetry, of less than about 26 weightpercent before being shaped, irradiated and crosslinked, b) xyleneextractables of less than or equal to about 70 weight percent, andwherein the article is in the form of an infection control item.
 14. Aheat-resistant, shaped and elastic article free of a silane crosslinkerand which comprises at least one ethylene interpolymer which has beenirradiated and crosslinked wherein the interpolymer comprises ethyleneinterpolymerized with at least one other monomer and is characterized ashaving: (a) an interpolymer density of less than or equal to 0.89 g/cm³or a DSC crystallinity at 23° C., as determined using differentialscanning calorimetry, of less than about 26 weight percent before beingshaped, irradiated and crosslinked, (b) a percent permanent set of lessthan 60 at 23° C. and 200 percent strain when measured at a 2 milthickness using an Instron tensiometer after being shaped, irradiatedand crosslinked, (c) a percent stress relaxation of less than or equal25 at 23° C. and 200 percent strain when measured at a 2 mil thicknessusing a Instron tensiometer after being shaped, irradiated andcrosslinked, (d) a percent stress relaxation of less than or equal 55 at38° C. and 200 percent strain when measured at a 2 mil thickness usingan Instron tensiometer after being shaped, irradiated and crosslinked,and wherein the article is in the form of an infection control item.